1. Field of the Invention
The present invention relates to an assembly substrate which contains a plurality of individual substrates in its surface direction, and its manufacturing method.
2. Description of the Related Art
In recent years, with the progress of electronics technology, there has been a growing demand towards higher density in printed circuit boards. As such, multilayer printed circuit boards in which are laminated pluralities of wiring patterns and insulating layers are becoming widely used.
Conventionally, for the purpose of increasing productivity, printed circuit boards used in these types of applications are manufactured in a “multiple dice from one substrate” manner in which, for example, an approximately 300 mm to 500 mm square worksheet (assembly substrate) provided with a plurality of wiring pattern groups (wiring layers) for printed circuit boards is separated into individual dice by dicing or the like to obtain a plurality of printed circuit boards (individual substrates, dice, or bodies). Multi-layering of the worksheet is normally achieved by alternately building up wiring patterns and insulating layers. Then, generally, a wiring pattern or the like is formed using a subtractive method or an additive method while an insulating layer is formed by thermal curing of a thermosetting resin.
With the conventional worksheet manufacturing method described above, warpage of a worksheet inevitably occurs due to stress applied during the formation of the insulation layers. Therefore, in order to suppress the warpage of the worksheet, for example, Japanese Patent Laid-Open No. 2005-167141 proposes a manufacturing method for obtaining a plurality of individual substrates on which a plurality of wiring pattern groups (wiring layers) for printed circuit boards as well as a frame-like conductive pattern that is discontinuous with slits formed thereon and surrounds the plurality of wiring patterns are provided on a worksheet, and after processes such as build-up and surface-mounting, the worksheet is separated so as to remove the frame-like conductive pattern.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-167141
In recent years, for the purpose of improving manufacturing efficiency, a method under consideration for producing a plurality of individual substrates involves producing a large work board serving as an assembly substrate that contains a plurality of worksheets, separating the work board by a dicer or the like to produce a plurality of small worksheets, and further separating the resultant worksheets.
When the above-mentioned conventional manufacturing method is applied to the production of such work boards, since a frame-like conductive pattern is provided discontinuously, resultant work boards may have poor substrate strength in a portion not provided with frame-like conductive patterns, resulting in handling difficulty at the time of manufacturing/processing including transferring and separating as well as insufficient suppression of warpage. It is expected that these problems will be significant further as the work board becomes thinner and has a larger area.
On the other hand, with the frame-like conductive pattern removed, each of the worksheets obtained by separating the work board will have significantly lower substrate strength in comparison to the work board, resulting in handling difficulty and warpage which is not suppressed at all. As a result, inconveniences such as transfer failures and degraded positional accuracy at the time of build-up and surface mounting may occur. Therefore, when the above-mentioned conventional manufacturing method is applied to the production of a work board, not only reduction of productivity and economic efficiency, such as a decline in process yield, but also a decline in the mounting reliability will occur.